Blasting explosive



nited States Patent Cfiice 2,752,848 Patented July 3, 1956 BLASTINGnmmosrvn Application February 19, 1953, Serial No. 337,888

3 Claims. (Cl. 102-24) No Drawing.

The present invention relates to a novel explosive blasting cartridge,and to its manufacture.

At the present time, substantially all of the underground blastingoperations, such as in the mining industry, are carried out withconventional dynamite cartridges having a diameter of from to 1 /2inches, and a length of 8 inches. The dynamite compositions are based onnitroglycerin, which is present in a ratio of from 25 to 15% of theentire explosive. For special purpose blasting, cartridges as long as 12or 16 inches have been manufactured, but the 8 inch length constitutesthe usual cartridge size. The 1% inch diameter represents the largestdiameter considered practicable by the industries using undergroundblasting because of the expense in producing larger diameter boreholes,and the necessity of holes properly spaced for good fragmentation. Thisdiameter limitation has heretofore precluded the use ofnitroglycerin-free explosives, since the high-density charges ofdiameters under two inches would not propagate the detonation throughoutthe borehole. When the density was decreased, detonation could beobtained with the small diameters, but the loss of strength rendered thecharge unsuitable for underground work.

There are several serious objections to the nitroglycerin dynamiteswhich make a replacement thereof highly desirable. In loading longboreholes, it is frequently necessary to split the cartridge and tampthe composition into the hole. The operating personnel thus subjected tonitroglycerin liquid and vapor sufier from the severe headaches producedby nitroglycerin. The loading of the relatively soft dynamitecomposition into the borehole presents difficulties since it isessential that the explosive extend to the end of the borehole, and bepresent throughout in sufficient density for proper blasting action.Since many boreholes present rough sides, and are angled in variousdirections from the point of loading, the tamping operation requiresskill and careful supervision. The short length of the individualcartridge requires repeated withdrawals and replacement of the tampingrod or stick in the borehole.

It is an object of the present invention to provide a small diameterexplosive blasting cartridge which does not contain a nitroglycerincomposition. A further object is to provide rigid, high-density blastingexplosive cartridges in small diameters. A still further object is toprovide a method for manufacturing rigid, high-density blastingexplosive cartridges free from nitroglycerin which have the requisitesensitivity in small diameters. Additional objects will become apparentas the invention is further described.

We have found that the foregoing objects are attained, and anexplosivecartridge of the desired characteristics and dimensionsobtained when we package a composition containing at least 60% by weightof a mixture of ammonium nitrate and sodium nitrate, wherein theammonium nitrate constitutes from 30 to of the weight of the mixture, 10to 30% of a blend of dinitrotoluene and trinitrotoluene wherein thedinitrotoluene constitutes from 1 to 50% of the weight of the mixtureand not more than 10% of the weight of the entire composition, and from0.5 to 10% by weight of a finely divided metallic fuel.

The ammonium nitrate has a fineness such that at least 40% will passthrough a mesh screen. The bulk density of the entire amount of ammoniumnitrate present must be less than 0.95 gram per cubic centimeter. Whilethe fineness of the sodium nitrate is not as critical as that of theammonium nitrate, it is preferred that at least 50% pass a 48 meshscreen.

The cartridge is manufactured by first forming a blend of the substancesin the proportions set forth above at a temperature of at least about160 F., then slowly cooling, with constant stirring, the blend thusformed to a temperature between F. and F., and immediately packing atthe latter temperature to form a substantially cylindrical cartridgehaving a diameter of from 1 to 2 inches. The cartridge thus produced isrigid when cooled to ambient temperatures and has a density of from 1.3to 1.5 grams per cubic centimeter.

The cartridge may be made several feet in length, if desired, andpackaged in a shell of waterproof material such as paraffined paper,synthetic film, etc. The preferred procedure is to pack the heatedcomposition directly into the shell. However, the invention is notlimited with respect to the packaging material or to packing thecomposition directly into a waterproof shell.

The cartridge prepared as described above is a highvelocity,high-strength blasting explosive completely free from nitroglycerinwhich can be initiated by a cap-sensitive primer and will propagate thedetonation along a column within a borehole, in diameters as small asfrom 1 to 2 inches. The high density of the cartridge provides asufficient quantity of explosive composition per unit length of theborehole to approximately equal the blasting strength of an equivalentlength of tamped dynamite.

The composition of the charge may be varied over a considerable rangeprovided the high density, high velocity, and adequate sensitivity are,maintained.

The effects obtained by varying the proportions of the ingredients andby the omission or substitution of ingredients is illustrated in Table1, wherein the ingredients are listed as per cent by weight of the finalcomposition. The density is measured as grams per cubic centimeter andthe velocity as meters per second. In Examples 1 to 11 inclusive, thesensitivity was measured with full cartridges placed end to end, whilein Examples 12 to 18 inclusive, the cartridges were cut in half and thedistance the primer would consistently initiate the receptor wasmeasured. In Examples 19 to 23 inclusive, the cartridges were again endto end, but the ends were closed with metal foil. In all of theexamples, the cartridges had a diameter of 1% inches and a length offrom 18 to 24 inches.

The cartridges were prepared by mixing the ammonium nitrate and sodiumnitrate in a ribbon-type mixer at about 150 F., adding the ferrosiliconand raising the temperature of the mixture to F. At this point, themelted trinitrotoluene-dinitrotoluene blend was added, and theingredients mixed for 10 minutes at F. The mixture was slowly cooledwith constant mixing to between 120 F. and 140 F. and packed at thistempera ture into the shells to the density shown. The packing was doneby hand, the composition being tamped to the desired density.

TABLE I Dinitrotoluene Trinitrotoluene #3 Ammonium Nitrate #2 AmmoniumNitrate Example nium #4 Ammo- Nitrate Sensitivity Calcium StearateFerrosilicon Sodium Nitrate Density Velocity #mhwmmwwwoamww-mm es swwweeew ewoomm wwesm OQ'IUIUIQILAQOOOOOUIOOOOOOOOOO Propagation over anair gap. #1 Ammonium Nitrate:

On 20 mesh sereen1025%.

On 35 mesh sereen80%.

Through 65 mesh screen-5%.

#2 Ammonium Nitrate:

On 35 mesh sereen5%.

On 65 mesh sereen0-10%.

Tllloclgll 100 mesh screen55100%; bulk density-less than 0.90

From the foregoing table, the following conclusions can be drawn:

1) Mixtures having 10% or less of the mixture of trinitrotoluene anddinitrotoluene as illustrated in Examples l to 4 are not adequatelysensitive, and the absence of dinitrotoluene (Example 5) causes thedensity of the packed charge to be below the desired level. However,where the dinitrotoluene is present in an amount exceeding of the totalweight of the composition (Example 17), the resultant product will beinsensitive and will not propagate. Any of the commercial grades oftrinitrotoluene and dinitrotoluene may be used.

(2) The physical characteristics of the ammonium nitrate are ofimportance in determining the properties of the explosive. Example 21,utilizing only coarse ammonium nitrate, illustrates that suchcomposition will not propagate the detonation. Example 20, using a finerammonium nitrate than that of Example 21 shows some improvement, but isstill not sufficiently sensitive. When an ammonium nitrate of fine,regular grains, and a correspondingly higher density than 0.93 gram percubic centimeter, is used, as in Example 19, the sensitivity is stillnot adequate. The fine, irregularly shaped grains of ammonium nitratedesignated as ammonium nitrate #2, either in admixture with a coarseammonium nitrate as in Examples 6 and 10, or with sodium nitrate as inExamples 11, 18, 22 and 23, produces the desired characteristics ofdensity, sensitivity and high velocity.

The effect of density on propagation and also the desirability of usingmetal closures on the ends is illustrated in Table 2, wherein the airgap was measured with the cartridges in an end-to-end relationship.

A cartridge having a density below 1.3 grams per cubic #3 AmmoniumNitrate:

On 35 mesh screen1520%. Through mesh screen1535%. #4 Ammonium Nitrate:

On 35 mesh screen05%. On 65 mesh sereen0-10%. Thr/ough 100 meshsereen55100%; bulk density-more than 0.93

g. cc.

centimeter can be prepared from the present compositions, but suchlow-density explosive cartridges are not suitable for undergroundblasting, and are therefore outside the scope of the present invention.

By the ballistic mortar test, the preferred composition, illustrated inExamples 11 and 22, is rated about 94% as strong as trinitrotoluene. Inactual field trials in hard granite rock, the same composition was foundto be equal to an ammonia semi-gelatin dynamite having a ballisticmortar rating of in comparison with TNT.

The packing density of the composition is a function of the packingtemperature. When packed at temperatures over 150 F., the density of thecartridge exceeds 1.5, while when packed at temperatures below F.,densities as high as 1.3 could not be consistently obtained.

The explosive cartridges of the present invention are thus substantiallyequal in strength to the nitroglycerin dynamites and have thedistinctive advantage over the nitroglycerin dynamites of being rigidand free from toxic effects on the users. An additional advantage isthat the present cartridges are much safer to handle since they are muchless sensitive to shock than the conventional dynamites. Because of thesafety features of this explosive, methods of packing the cartridges arenot so limited as in the case of nitroglycerin-containing compositionsand cartridges can be made in long lengths for example, 36 to 48 inches,without difficulty, and, due to their rigidity, used to tamp thepreceding cartridges into the borehole. Thus, for long boreholeshooting, they are much easier and safer to load.

While only ferrosilicon has been used in the examples, conventionalmetallic fuels such as aluminum, magnesium-aluminum alloys, andmagnesium silicide can be used just as satisfactorily. The ferrosiliconwill preferably contain at least 40% silicon. The following exampleillustrates the use of aluminum in the present composmon Example 24 Theprocedure described in connection with the examples listed in Table 1was followed, using the following ingredients:

20 parts trinitrotoluene, 4 parts dinitrotoluene, 30.2 parts #2 ammoniumnitrate, 42.7 parts of sodium nitrate, 2.0 parts of finely dividedaluminum, and 0.5 part of calcium stearate.

The composition had a velocity of 4165 meters per second at a density of1.3 grams per cubic centimeter. The sensitivity, measured by the air-gaptest, was 1 /2 inches with plain ends and over 7 inches with metalcovered ends.

The invention has been described in detail in the foregoing. Manyvariations and modifications may be made without departing from thescope of this invention. Therefore, we intend to be limited only by thefollowing claims.

We claim:

1. A blasting cartridge comprising a substantially cylindrical chargehaving at least 60% by weight of a mixture of ammonium nitrate andsodium nitrate, the proportion of ammonium nitrate in said mixture beingfrom to 85% and the ammonium nitrate having a bulk density of less than0.95 gram per cubic centimeter and at least thereof passing a 100 meshscreen, over 10% and up to 30% by weight of a blend of dinitrotolueneand trinitrotoluene, the proportion of dinitrotoluene in the blend beingfrom 1 to but not exceeding 10% by weight of the entire charge, and from0.5 to 10% by weight of a finely divided metallic fuel, said chargehaving a diameter of from 1 to 2 inches and a density of from 1.3 to 1.5grams per cubic centimeter.

2. A blasting cartridge as claimed in claim 1 wherein the finely dividedmetallic fuel is a ferrosilicon having at least 40% silicon.

3. A method for the cartridging of a detonating explo sive compositioncontaining at least by weight of a mixture of ammonium nitrate andsodium nitrate, the proportion of ammonium nitrate by weight in saidmixture being from 30 to and the ammonium nitrate having a bulk densityof less than 0.95 gram per cubic centimeter and at least 40% thereofpassing a mesh screen, over 10% and up to 30% by weight of a blend oftrinitrotoluene and dinitrotoluene, the proportion of dinitrotoluenebeing from 1 to 50% but not exceeding 10% of the weight of the entirecharge, and from 0.5 to 10% by weight of a finely divided metallic fuel,which comprises heating said composition to a temperature of at least160 F., cooling said charge slowly and with constant stirring to atemperature of between and F., and packing at this temperature into asubstantially cylindrical form having a diameter of from 1 to 2 inchesto a density of from 1.3 to 1.5 grams per cubic centimeter.

References Cited in the file of this patent UNITED STATES PATENTS393,634 Favier Nov. 27, 1888 1,992,217 Kirst et al. Feb. 26, 19352,069,612 Kirst et a1 Feb. 2, 1937 2,087,285 Handforth et al. July 20,1937 2,168,562 Davis Aug. 8, 1939 2,602,732 Farr July 8, 1952

1. A BLASTING CARTRIDGE COMPRISING A SUBSTANTIALLY CYLINDRICAL CHARGEHAVING AT LEAST 60% BY WEIGHT OF A MIXTURE OF AMMONIUM NITRATE ANDSODIUM NITRATE, THE PROPORTION OF AMMONIUM NITRATE IN SAID MIXTURE BEINGFROM 30 TO 85% AND THE AMMONIUM NITRATE HAVING A BULK DENSITY OF LESSTHAN 0.95 GRAM PER CUBIC CENTIMETER AND AT LEAST 40% THEREOF PASSING A100 MESH SCREEN, OVER 10% AND UP TO 30% BY WEIGHT OF A BLEND OFDINITROTOLUENE AND TRINTROTOLUENE, THE PROPORTION OF DINITROTOLUENE ANDBLEND BEING FROM 1 TO 5% BUT NOT EXCEEDING 10% BY WEIGHT OF THE ENTIRECHARGE, AND FROM 0.5 TO 10% BY WEIGHT OF A FINELY DIVIDED METALLIC FUEL,SAID CHARGE HAVING A DIAMETER OF FROM 1 TO 2 INCHES AND A DENSITY OFFROM 1.3 TO 1.5 GRAMS PER CUBIC CENTIMETER.